Patent GB-532066-A (GB)
Title: Improvements in or relating to thermionic valve circuits
IPC: H03F1/54
Filed: 1939-08-15
Abstract: 532,066. Thermionic valve circuits; repeaters. SIEMENS BROS. & CO., Ltd., LONG, D. P., PETERS, C. L., and CRUTCH, L. S. Aug. 15, 1939, No. 23556. [Class 40 (v)] [Also in Group XXXIX] A thermionic valve circuit especially for unattended repeaters comprising two or more valves forming a group and connected for the performance of a task which each is capable of performing singly is provided with switching relays controlled by the direct currents emitted by each valve respectively and controlling the cathode heating circuits of the valves in such a way that when one valve emits its proper direct current the cathode heating circuits of the other valves are open. These valves are thus held in reserve, and one of them only is switched in automatically if the valve that was in operation fails. As shown in Fig. 1, three sets of relays A, AX, B, BX, C, CX are inserted in the anode circuit of three valves VA, VB, VC between the anodes and a common output transformer (not shown) in the line OT ; and three resistances CA, CB, CC are provided for the heater circuits. When the valve VA operates, the relays A, AX cause the anode and heater circuits of the other valves to be cut off and the resistance CA to put across the heater mains HS to take current in place of the heaters of the cut off valves. If anode current of valve VA falls below a given value, the relays A, AX cause valve VB to operate and the relays B, BX put the other valves out of circuit; and so on when valve VB fails. In a modification, Fig. 2, a three winding transformer TR (I), TR(II), TR(III) is interposed between the anodes and relays (not shown) similar to the relays of Fig. 1 in the lines LA, LB, LC. When the valve VC operates, the winding TR(III) acts as a choke and the output signal is taken through a condenser QL. When one of the other valves operates, the windings act as transformer windings, and the output signal is taken from winding TR(III) acting as a secondary and again through condenser QL. In this arrangement, the resistances CA, CB, CC of Fig. 1 are omitted. In another modification the relays are inserted next to the biasing resistances of the cathodes. When a second set of valves follows a previous set, the heater circuit of the second set is switched off by the relays of the first set if more than one valve of the first set is in operation as may occur in starting. The condition of the valves may be indicated at a distant station by means of contacts a3, b3, c3, Fig. 1, operated by the relays of the respective valves to effect circuit changes in a supervisory apparatus STU. For example, as shown in Fig. 5, the contacts a3, b3, c3 may connect up various tappings of a coil TL to vary the tuning of a circuit including that coil and a condenser TC. The tuning of this coil circuit is determined at a distant station SHS by means of a bridge circuit including a centre tapped transformer T in two arms and an artificial line BN to balance the line SCA between the two stations. Alternatively, the tuned circuits controlled by the contacts a3, b3, c3 are arranged to affect the attenuation characteristics of the transmission circuit and this is detecting by a testing operation between two distant stations.